Ammonia recycling still for a refrigeration system and method therefor

ABSTRACT

An ammonia still apparatus of the invention is used to reclaim ammonia from contaminated ammonia refrigeration fluid in an ammonia refrigeration system. The ammonia still apparatus is used in fluid communication with the ammonia refrigeration system and can be run manually or automatically using an electronic controller, such as a programmable logic controller. The ammonia is separated from the contaminated refrigeration fluid after heating the fluid with a heat exchanger. The reclaimed ammonia is returned to the ammonia refrigeration system where it is reused. Waste fluid from the ammonia still apparatus is collected and dumped.

PRIORITY

The present application claims the benefit of U.S. ProvisionalApplication No. 60/704,097 filed on Jul. 29, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ammonia still apparatus and methodfor purifying ammonia from contaminated refrigeration fluid.

2. Description of the Prior Art

In the classic compression type refrigeration system, a refrigerant isalternately compressed and expanded. In a simple closed loop compressiontype refrigeration system, there is at least a compressor, anevaporator, a throttling or metering device, and a condenser. During onestage of the compression type refrigeration cycle, a low pressurerefrigerant vapor enters the compressor. At this point in the cycle,work is required of the compressor in order to raise the pressure andthe boiling point of the refrigerant vapor. In the next phase of thecompression type refrigeration cycle, the high pressure, hightemperature refrigerant vapor leaving the compressor is transferredthrough a heat exchanger called a condenser. A second fluid passesthrough the condenser in order to remove heat from the refrigerantvapor, thereby transforming the refrigerant vapor to a refrigerantliquid. As the refrigerant liquid exits the condenser, it leaves at thesame pressure but at a lower temperature than it had upon entering thecondenser.

Next, the refrigerant passes through a throttling device that reducesthe pressure, temperature and boiling point of the fluid. In the laststep of the typical compression type refrigeration cycle, refrigeranttravels through an evaporator to receive heat from some other fluid incommunication with the evaporator to achieve the desired cooling effectof this other fluid. Such a closed loop compression refrigeration cycleis duplicated in order to repetitively remove heat from a body of fluidin communication with the evaporator.

Commercial and industrial refrigeration systems typically use anhydrousammonia. Anhydrous ammonia is the liquid form of pure ammonia gas and istechnically water-free. Most refrigeration experts consider industrialgrade anhydrous ammonia to be the most economical and efficient heattransfer medium for industrial refrigeration processes.

Water, unfortunately, finds its way into the refrigeration system, andover time, accumulates to a level of concern. Ammonia readily associateswith water to form ammonium hydroxide, an inferior refrigerant thatreduces the efficiency of the refrigeration system. The reducedefficiency increases the use of energy consumed in the system, thusincreasing the cost of operation and also accelerates wear and tear onequipment causing shorter mean time to failure.

In an industrial refrigeration system, compressors, piping, and vesselscontaining anhydrous ammonia are prevalent throughout the refrigerationplant. Such a refrigeration system generally has lubricating oilsinserted into the compressor for lubrication. Invariably, some of theoil or other lubricant migrates throughout the system, mixing with theanhydrous ammonia. Since the oil serves as an insulator or retardant toheat transfer, a high prevalence of waste oil in a refrigeration systemcompromises the efficiency of the refrigeration process. In addition,chemical reactions can occur between the oil, ammonia and/or water toproduce additional waste products, such as sludge and acids. Theaddition of oil and water to ammonia can also provide a rich medium formicrobiological growth which can produce slime and acids to furtherdegrade the efficiency of operation as well as physically damage thesystem.

In order to prevent deterioration of the refrigeration efficiency aswell as the physical parts of the system, accumulations of wastelubricating oil and water need to be purged from the system. Mostcommercial and industrial refrigeration units include one or more portslocated at a lower level in the piping system and arranged such thatlubricating oil will accumulate there to be drained from the pipes forcollection and/or discarding. Unfortunately, the ammonia is wasted inthese systems.

Therefore a need exists to purify and recycle ammonia in a refrigerationsystem from waste fluid having waste oil and water contaminants whilepreventing the undesirable side effects associated with draining wastefluid.

SUMMARY

The ammonia still apparatus of the invention is used to purify andrecycle anhydrous ammonia from contaminated ammonia refrigerant fluid inan ammonia refrigeration system. The apparatus and method of using theapparatus reclaims ammonia from oil, water and other contaminants in therefrigeration fluid. The reclaimed ammonia is then recycled back intothe refrigeration system. Therefore, the ammonia still apparatusconnects to the refrigeration system for receiving contaminatedrefrigeration fluid and recycling purified ammonia back into therefrigeration system and can be used manually or in an automatic modewith an electronic controller, such as a programmable logic controller(PLC).

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself however, as well as apreferred mode of use, further objects and advantages thereof, will bestbe understood by reference to the following detailed description of anillustrative embodiment when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is front plan view of the ammonia still apparatus of theinvention with the electrical lines removed for easier viewing;

FIG. 2 is a side plan view of the ammonia still apparatus of theinvention with the electrical lines removed for easier viewing;

FIG. 3 is a top plan view of the ammonia still apparatus of theinvention with the ammonia discharge line removed; and

FIG. 4 is a side plan view of the ammonia still apparatus of theinvention with additional valves for access to the apparatus andelectrical lines drawn schematically.

DETAILED DESCRIPTION OF THE INVENTION

Turning to the Figures, where like reference numerals refer to likestructures, an ammonia still apparatus 10 of the invention is used topurify and recycle anhydrous ammonia from contaminated ammoniarefrigerant fluid. The ammonia still apparatus 10 is in fluidcommunication with an ammonia refrigeration system 12 and can be usedmanually with or without an electronic controller, such as aprogrammable logic controller (PLC) 14 to control the operations of theammonia still apparatus 10. The PLC 14 is communication with the ammoniastill apparatus 10 and is preferably part of the ammonia still apparatus10, although the PLC 14 can be installed in another location and wiredto the ammonia still apparatus 10.

During manual operation with the PLC 14, a solenoid energizes to open avalve immediately in response to a pushbutton input from the controlpanel 16 of the PLC 14, once a particular function is selected. In thisdisclosure, the term “solenoid” is used to refer to a solenoid or thecombination of the solenoid and the valve the solenoid controls. Uponrelease of the pushbuttons, the solenoid de-energizes and the valvecloses.

The PLC 14 can be programmed to control the solenoids in the ammoniastill apparatus 10. The PLC 14, for example, can be programmed to havethe following functions in response to the input from particularprogrammed function keys. For example, FI is programmed to energize asuction solenoid 50. F2 is programmed to energize the liquid solenoid22. F3 is programmed to energize a hot gas solenoid 60. F4 is programmedto energize a discharge solenoid 72. F5 is programmed to energize awater dump solenoid 88.

The solenoids open immediately in response to switching a selectorswitch 18 on the front of the control panel 16 from manual operation toautomatic operation. Once in automatic operation, the suction solenoid50 and liquid solenoid 22 energize and their valves open. Contaminatedammonia refrigerant fluid flows from the ammonia refrigeration system 12through a liquid inlet 20 into a tank 26. The liquid inlet 20 has aliquid solenoid 22, preferably with a strainer, that controls the flowof contaminated fluid into the ammonia still apparatus 10.

The tank 26 has an upper tank 28, such as a vertical pipe, in fluidcommunication with the liquid inlet 20, an ammonia line 40 and a lowertank 30, such as a horizontal pipe. The upper tank 28 can have a cap 32covering the top with an upper opening 34 for receiving a plug 36 or asafety relief valve. At the bottom of the lower tank 30 is a tank outlet38. If desired, the tank 26 can be insulated.

Contaminated ammonia refrigerant fluid flowing into the tank 26 can bemeasured with an upper liquid sensor 42, such as a float switch 44. Thefloat switch 44 is in communication with the PLC 14 and in fluidcommunication with the tank 26. The contaminated fluid level in the tank26 rises until reaching a set maximum level. Then the float switch 44signals to the PLC 14 that the contaminated fluid is at the maximumlevel. The PLC 14 de-energizes the liquid solenoid 22 and closes itsvalve to stop the flow of contaminated fluid into the tank 26. Thesuction solenoid 50 remains energized and open.

The float switch 44 has an upper float line 46 and a lower float line47. The upper float line 46 is in fluid communication with the uppertank 28. The lower float line 47 is in fluid communication with the tankoutlet 38. When the contaminated fluid level in the tank 26 rises, afloat rod in the float switch 44 also rises until reaching the maximumfluid level. At the maximum fluid level, the float switch 44 signals thePLC 14 and switches off the flow of contaminated fluid into the tank 26.

As soon as the liquid solenoid 22 de-energizes and closes, the PLC 14activates a heat exchanger 48 in fluid communication with the tank 26.The heat exchanger 48 has a heat exchanger fluid inlet 54 and a wastefluid outlet 56 at the opposite end for discharging waste fluid, such aswater and oil. The heat exchanger 48 heats the contaminated fluid fromthe tank 26 to boil off anhydrous ammonia. The heat exchanger 48 shouldmaintain a temperature of about 60° F., but can be set at a temperaturerange of about 0° F. to about 100° F., with a preferable range of about60° F. to about 65° F. Once reaching the boiling point of ammonia,anhydrous ammonia boils and separates from the heated contaminatedfluid. The anhydrous ammonia passes upward through the contaminatedfluid and back into the tank 26. The anhydrous ammonia discharges fromthe tank 26 through the ammonia discharge line 40 and back into therefrigeration system 12 where it is reused. The ammonia discharge line40 has the suction solenoid valve 50 which opens to allow the anhydrousammonia out of the ammonia still apparatus 10. An ammonia regulator 52in the ammonia discharge line 40 can control the pressure of theanhydrous ammonia.

The heat exchanger 48 is preferably a fluid heat exchanger 58 using hotgas, such as ammonia, available from the plant to heat the contaminatedfluid. The PLC 14 energizes a hot gas solenoid 60 and its valve opens toallow hot gas to flow through the hot gas inlet 62 into the heatexchanger 58. A hot gas regulator 64 can control the pressure in the hotgas inlet 62, typically between about 100 psi to about 120 psi.

The hot gas heats the contaminated fluid, and in doing so, cools and cancondense. The condensate flows out of the heat exchanger 58 though adischarge outlet 66. The discharge outlet 66 can have a drain trap 68leading to a drain 70 in fluid communication with the plant. A dischargesolenoid 72 communicates with the PLC 14, which controls the energizingof the discharge solenoid 72 and the opening of its valve to returnliquid condensate to the plant.

Upper and lower temperature sensors 74, 76 are located at opposite endsof the heat exchanger 54. The temperature sensors 74, 76 measure thetemperature of the fluid at both ends of the heat exchanger 54 andcommunicate the measured temperatures to the PLC 14. The uppertemperature sensor 74 measures the upper temperature of the contaminatedfluid between the tank 26 and the heat exchanger 54, such as at a firstfitting 78 connecting the tank outlet 38, a heat exchanger fluid inlet54 and the lower float line 47. The lower temperature sensor 76 measuresthe lower temperature of the waste fluid discharged from the heatexchanger 54, preferably at a second fitting 80 connecting the wastefluid outlet 56 with a water/oil discharge line 82 and a lower liquidsensor 84, such as a liquid switch 81.

If the lower temperature sensor 76 and the upper temperature sensor 74signal the PLC 14 that the temperatures of the contaminated fluid andthe waste fluid have reached the temperature set point (which can beshown on the PLC 14 display screen) but the tank fluid level in the tank26 has not reached the set maximum tank fluid level measured by theupper liquid sensor 42, the system repeats the process from thebeginning. Alternatively, if the upper and lower temperature sensors 74,76 are not equal and the tank fluid level in the tank 26 has not reachedthe set maximum level, the cycle restarts. To restart the cycle, the hotgas solenoid 60 and the discharge solenoid 72 de-energize and closewhile the liquid solenoid 22 energizes and opens again until the tankfluid level in the tank 26 reaches the maximum level.

The system repeats the cycle until the upper and lower temperaturesensors 74, 76 signal the PLC 14 that the upper and lower temperaturesare equal. Once the upper and lower temperatures are equal and the tankfluid level in the tank 26 reaches the upper level switch 42, theammonia still apparatus 10 is ready to discharge the waste fluid whichhas been collecting.

At this point, the PLC 14 signals the hot gas solenoid 60, the suctionsolenoid 50 and the discharge solenoid 72 to de-energize and close. Thewater fill solenoid 86 for an oil skimmer tank 92 now energizes andopens its valve to send fresh water into the oil skimmer tank 92. Aftera period of time, such as five minutes, the waste dump solenoid 88energizes and opens its valve to dump the waste fluid into the oilskimmer tank 92 and the suction solenoid 50 de-energizes and closes. Thewater fill solenoid 86 remains energized during this time. A flow meter90 measures the flow of the waste fluid from the ammonia still apparatus10 and an associated throttling valve can regulate the rate of flow.

When the lower liquid sensor 84 for the water dump reaches its set lowerwaste fluid level point, the lower liquid sensor 84 sends a signal backto the PLC 14. The PLC 14 signals the water dump solenoid 88 and waterfill solenoid 86 to de-energize and close. The cycle begins again byenergizing and opening the suction and liquid solenoids 50, 22.

In the oil skimmer tank 92, the oil is allowed to separate from thewater. Fresh water can flow into the oil skimmer tank 92 to help diluteany remaining ammonia by absorbing it into a larger mass of water andpreventing undesirable odor in the installed location. The separated oilis drawn off into an oil receiver 95, such as a bucket. An oil flowmeter 94 in fluid communication with the oil line 98 can measure theamount of oil collected and send the measured amount to the PLC 14. Anoil level sensor switch 96 in communication with the PLC 14 could alsobe used to turn off the ammonia still apparatus 10 if the oil receiver94 is filled. The separated oil can then be collected and disposedseparately from the water.

The number of gallons of water dumped from the system is displayed onthe display screen of the PLC 14. Alternatively, the number of gallonsdumped can be sent to a networked computer or printer, as well as otherdata which can be collected, such as temperature and pressure.

The PLC can be programmed from the control panel in the program mode orrun in a previously programmed mode. The PLC can also be part of acomputer network and can be remotely programmed from the network. Theprogram mode allows maximum flexibility to alter the parameters of thesystem to match the conditions of the plant and fluid. The PLC can alsobe programmed to draw fluid from different points in the refrigerationsystem. The run mode allows the continuous running of the ammonia stillapparatus of the invention without requiring an operator to monitor anddump out the system. This also allows the ammonia still apparatus to runwhile providing shut-offs and safeguards to the system.

The display screen can constantly show the upper and lower sensortemperatures, the number of gallons of water dumped from the system andthe temperature set point. The temperature set point is the same forboth the upper and lower sensors. Once the system is in the run mode,the display screen can show the current conditions of the system, suchas the upper and lower temperatures, the temperature set point and thegallons of water produced.

Regulators can be used in the hot gas and ammonia lines to controlpressure if desired. Pressure sensors can also be used to send feed backto the PLC 14 and monitor the pressure in the system. Additional valves100, 101, 102 can be used in the lines for additional access to theammonia still apparatus for safety.

The ammonia still apparatus of the invention allows the ammoniarefrigerant to be purified over time for greater efficiency in theoperation of the refrigeration system. As a result, the refrigerationsystem requires fewer compressors, smaller equipment and higherpressures to maintain adequate temperatures in the facility. Thisgreatly decreases energy costs and other expenses, such as systemcleaning and pipe replacement, and reduces wear and tear on theequipment.

While the invention is shown in only one of its forms, it is not thuslimited but is susceptible to various changes and modifications withoutdeparting from the spirit and scope of the invention.

1. An ammonia still apparatus for an ammonia refrigeration system,comprising: a liquid inlet; a tank in fluid communication with theliquid inlet; an ammonia discharge line in fluid communication with thetank; a heat exchanger in fluid communication with the tank; an uppertemperature sensor being located between the tank and the heatexchanger; an upper liquid sensor in fluid communication with the tank;a waste fluid outlet in fluid communication with the heat exchanger; alower liquid sensor in fluid communication with the waste fluid outlet;a water/oil discharge line in fluid communication with the waste fluidoutlet; a lower temperature sensor being located between the heatexchanger and the water/oil discharge line.
 2. An ammonia stillapparatus of claim 1, further comprising: a PLC in communication withthe upper and lower temperature sensors and the upper and lower liquidsensors. a liquid solenoid in fluid communication with the liquid inletand in communication with the PLC; and a suction solenoid in fluidcommunication with the ammonia discharge line and in communication withthe PLC.
 3. An ammonia still apparatus of claim 2, wherein the water/oildischarge line further comprises: a waste dump solenoid in communicationwith the PLC; and a flow meter in communication with the PLC.
 4. Anammonia still apparatus of claim 3, wherein the upper liquid sensor is afloat switch in communication with the PLC, and the lower liquid sensoris a liquid switch in communication with the PLC.
 5. An ammonia stillapparatus of claim 4, further comprising: an oil skimmer tank in fluidcommunication with the water/oil discharge line; and a water fillsolenoid in communication with the PLC and in fluid communication withthe oil skimmer tank.
 6. An ammonia still apparatus of claim 1, furthercomprising: further comprising: a hot gas inlet in fluid communicationwith the upper end of the heat exchanger; and a discharge outlet influid communication with the lower end of the heat exchanger.
 7. Anammonia still apparatus of claim 6, further comprising: a PLC incommunication with the upper and lower temperature sensors and the upperand lower liquid sensors; a liquid solenoid in fluid communication withthe liquid inlet and in communication with the PLC; a suction solenoidin fluid communication with the ammonia discharge line and incommunication with the PLC; and a waste dump solenoid in fluidcommunication with the water/oil discharge line and in communicationwith the PLC.
 8. An ammonia still apparatus of claim 7, furthercomprising: a flow meter in fluid communication with the water/oildischarge line and in communication with the PLC; an oil skimmer tank influid communication with the water/oil discharge line; and a water fillsolenoid in communication with the PLC and in fluid communication withthe oil skimmer tank.
 9. An ammonia still apparatus of claim 8, whereinthe upper liquid sensor is a float switch in communication with the PLC,and the lower liquid sensor is a liquid switch in communication with thePLC.
 10. An ammonia still apparatus for an ammonia refrigeration system,comprising: a PLC; a liquid inlet being in fluid communication with therefrigeration system and having a liquid solenoid in communication withthe PLC; a tank in fluid communication with the liquid inlet; an upperliquid float switch in fluid communication with the tank; an ammoniadischarge line in fluid communication with the tank and therefrigeration system and having a suction solenoid in communication withthe PLC; a heat exchanger in fluid communication with the tank; an uppertemperature sensor being located between the tank and the heatexchanger; a waste fluid outlet in fluid communication with the heatexchanger; a lower liquid sensor in fluid communication with the wastefluid outlet and in communication with the PLC; a water/oil dischargeline in fluid communication with the waste fluid outlet and having awater dump solenoid in communication with the PLC; and a lowertemperature sensor being located between the heat exchanger and thewater/oil discharge line and in communication with the PLC.
 11. Anammonia still apparatus for an ammonia refrigeration system of claim 10,further comprising: a hot gas inlet in fluid communication with theupper end of the heat exchanger and having a hot gas solenoid incommunication with the PLC; and a discharge outlet in fluidcommunication with the heat exchanger and having a discharge solenoid incommunication with the PLC.
 12. An ammonia still apparatus for anammonia refrigeration system of claim 11, wherein the hot gas inlet andthe discharge outlet are in fluid communication with the refrigerationsystem.
 13. An ammonia still apparatus for an ammonia refrigerationsystem of claim 12, wherein the water/oil discharge line furthercomprises: a water dump solenoid; a flow meter; and wherein the waterfill solenoid, the water dump solenoid, and the flow meter are incommunication with the PLC
 14. An ammonia still apparatus for an ammoniarefrigeration system of claim 13, further comprising: an oil skimmertank in fluid communication with the water/oil discharge line; and awater fill solenoid in fluid communication with the PLC.
 15. An ammoniastill apparatus for an ammonia refrigeration system of claim 14, furthercomprising: an oil receiver; and an oil line between the oil skimmertank and the oil receiver, the oil line having an oil flow meter incommunication with the PLC.
 16. A method of purifying ammonia fromcontaminated refrigeration fluid in an ammonia refrigeration system, themethod comprising the steps of: (a) allowing contaminated refrigerationfluid from the refrigeration system to flow into the tank; (b) heatingthe contaminated refrigeration fluid from the tank with a heat exchangerand preventing the contaminated refrigeration fluid from flowing intothe tank during heating; (c) measuring the contaminated refrigerationfluid level in the tank; (d) separating anhydrous ammonia from thecontaminated refrigeration fluid; (e) removing the separated anhydrousammonia; (f) returning the removed anhydrous ammonia from the tank tothe ammonia refrigeration system; (g) measuring an upper temperature ofthe contaminated refrigeration fluid between the tank and the heatexchanger; (h) measuring a lower temperature of the waste fluid afterleaving the heat exchanger; (i) measuring a tank fluid level in thetank; (j) discharging waste fluid from the heat exchanger once the uppertemperature and the lower temperature are equal and the tank fluid levelreaches a set maximum tank fluid level; and (k) preventing contaminatedrefrigeration fluid from flowing into the tank and anhydrous ammoniafrom leaving the tank during the discharge of waste fluid.
 17. A methodof purifying ammonia from contaminated refrigeration fluid in an ammoniarefrigeration system of claim 16, further comprising the steps of (l)measuring a waste fluid level of the waste fluid after leaving the heatexchanger; and (m) preventing the waste fluid from discharging once thewaste fluid level reaches a set lower waste fluid level point.
 18. Amethod of purifying ammonia from contaminated refrigeration fluid in anammonia refrigeration system of claim 17, further comprising the stepsof: (n) collecting the waste fluid in an oil skimmer tank; (o)separating oil and water from the waste fluid; (p) removing the oil; and(q) removing the water.
 19. A method of purifying ammonia fromcontaminated refrigeration fluid in an ammonia refrigeration system ofclaim 17, further comprising the steps of: (n) circulating hot gas inthe heat exchanger; (o) discharging hot gas condensate from the heatexchanger; and (p) preventing hot gas from circulating and hot gascondensate from discharging during the discharge of waste fluid.
 20. Amethod of purifying ammonia from contaminated refrigeration fluid withinan ammonia refrigeration system, the method comprising the steps of: (a)opening a liquid solenoid and allowing the contaminated refrigerationfluid to flow into a tank from the refrigeration system; (b) opening asuction solenoid and allowing anhydrous ammonia to flow from the tankinto the ammonia refrigeration system; (c) measuring a tank fluid levelof the contaminated refrigeration fluid level within the tank with anupper liquid sensor; (d) communicating the measured tank fluid level toa PLC; (e) heating contaminated refrigeration fluid from the tank with aheat exchanger; (f) closing the liquid solenoid during heating with theheat exchanger; (g) separating anhydrous ammonia from the contaminatedrefrigeration fluid in the heat exchanger; (h) sending the separatedanhydrous ammonia into the refrigeration system; (i) measuring an uppertemperature of the contaminated refrigeration fluid between the tank andthe heat exchanger; (j) measuring a lower temperature of the waste fluidafter leaving the heat exchanger; (k) communicating the measured upperand lower temperatures to the PLC; (l) measuring a waste fluid level ofthe waste fluid with a lower liquid sensor communicating with the PLC;and (m) opening a waste dump solenoid and discharging waste fluid fromthe heat exchanger after the upper and lower temperatures are equal andthe tank level reaches a maximum tank level; (n) closing the liquidsolenoid and the suction solenoid during waste fluid removal; and (o)wherein the PLC communicates with at least one of the solenoids to openand close the solenoids.
 21. A method of purifying ammonia fromcontaminated refrigeration fluid in an ammonia refrigeration system ofclaim 20, further comprising the steps of (p) measuring a waste fluidlevel of the waste fluid after leaving the heat exchanger; and (q)closing the waste dump solenoid once the waste fluid level reaches a setlower waste fluid level point.
 22. A method of purifying ammonia fromcontaminated refrigeration fluid in an ammonia refrigeration system ofclaim 21, further comprising the steps of: (r) collecting waste fluid inan oil skimmer tank; (s) separating oil and water from the waste fluid;(t) removing the oil; and (u) removing the water.
 23. A method ofpurifying ammonia from contaminated refrigeration fluid in an ammoniarefrigeration system of claim 21, further comprising the steps of: (r)opening a hot gas solenoid; (s) circulating hot gas in the heatexchanger; (t) opening a discharge solenoid to dispose of condensatefrom the heat exchanger; and (u) closing the hot gas and dischargesolenoids during waste fluid removal.